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judge-client-3

This is a HustOJ judge_client drop-in replacement based on systemd.

Why number "3"?

The HustOJ instance running on https://acm.xidian.edu.cn/ is our 2nd iteration for Xidian University Programming Contest Training Base Online Judge. So we number this iteration "3". We'll gradually replace more HustOJ components to make a 4th iteration.

How to use

DATABASE_URL=mysql://user:password@localhost/jol?socket=/run/mysqld/mysqld.sock cargo build --release --features=hustoj
sudo install -vm755 target/release/judge-client-3 /usr/bin
mv /usr/bin/judge_client{,.old}
ln -sv judge-client-3 /usr/bin/judge_client

Then custom judge3.toml (use mocktest/etc/judge3.toml as an example) and put it into $OJ_BASE/etc.

We rely on systemd slices for limiting CPU core numbers. Custom the files in etc/systemd/ and install them into /etc/systemd.

And you need to modify HustOJ Web interface code to add "No Output" and "Judgement Failed" verdicts.

Advantages

The most significant advantage is we are using a more modern judging mechanism:

  • We don't rely on a very strict system call whitelist. So we won't suddenly blow up after a glibc/libstdc++ upgradation.
  • We use an implementation suitable for all languages. On the contrary, the origin judge_client needs special case for Java or Python, etc.
    • So we can support more languages (even MATLAB may be supported with a license and a correct configuration, I believe).
    • judge_client relies on deprecated JVM feature for Java.
  • We don't use ptrace, so we have a better performance for problems with many system calls (heavy I/O, for example).
  • Our approach is more similar to DOMJudge so we can measure the time usage of solutions of problems for onsite contests, and use the result as a good approximation.

Disadvantages

  • Only functional with systemd-249 or later (so you need a state-of-art distro like Ubuntu 22.04).
  • No memory usage measurement or MLE report.
    • Memory limit is implemented but a submission exceeding the limit will be judged as RE.
    • Actually there is no reliable way to determine if an RE should be considered MLE. Competitive programming code often has no error handling paths so a NULL value returned by malloc, or a std::bad_alloc instance will lead to RE instead of MLE. So the origin HustOJ implementation also can't report MLE reliably.
  • Not as fast as original judge_client for very simple C/C++ programs (like hello world programs).